1. Field of the Invention
This invention relates to a communication apparatus and, more particularly, to a communication apparatus connected to a two-way communication line such as a common pay station line and having an audio and video communication function, such as a communication apparatus which includes a picture communicating telephone referred to as a visual telephone or conference telephone.
2. Description of the Related Art
FIG. 11 is a block diagram illustrating the general construction of a telephone having a picture communication function and illustrating an example of the conventional communication apparatus. Shown in FIG. 8 are a camera input unit 1, a display unit 2, a video input/output interface 3, a video coding/decoding unit 6 comprising a video coder 6a and a video decoder 6b, a microphone input unit 8, a speaker 9, an audio input/output interface 11, an audio coding/decoding unit 12 comprising an audio coder 12a and an audio decoder 12b, a control panel 13, a system controller 14, a separating multiplexer 15, a line interface 16, and a communication interface 17.
The operation of the prior art will now be described. The input image from the camera input unit 1 enters the video coder 6a through the video input/output interface 3. At the same time, input audio from the microphone input unit 8 enters the audio coder 12a through the audio input/output interface 11. The input image coded by the video coder 6a and the input audio coded by the audio coder 12a are multiplexed by the separating multiplexer 15 and transmitted to the communication line 17 via the line interface 16.
Meanwhile, a received signal from the communication line 17 enters the separating multiplexer 15 through the line interface 16, the multiplexer 15 separates the signal into an image signal and an audio signal, and the image and audio signals enter the video decoder 6b and the audio decoder 12b. The received image decoded by the video decoder 6b is displayed on the display unit 2 via the video input/output interface 3, and the received audio decoded by the audio decoder 12b is outputted to the speaker 9 via the audio input/output interface 11.
With the example of the prior art described above, however, optimum reproduction of the received image or received audio cannot be achieved. Moreover, the manner in which the transmitted image or transmitted audio is being transmitted to the receiving side cannot be verified, and therefore optimum coding also cannot be achieved. These problems are believed to result from certain deficiencies in the prior art, which will now be described.
First, with regard to picture communication, the conventional apparatus is not equipped with means for adjusting coding or decoding parameters. As a consequence, picture quality cannot be set at will. In addition, the input image from a camera and an image (hereinafter referred to as a coded image) which has undergone coding and decoding processing cannot be displayed simultaneously on the same display screen.
As for audio communication, the input audio and audio obtained by coding, returning and decoding this input audio cannot be outputted as audio or displayed on a display screen (as in the form of a spectrum) simultaneously or separately. In addition, audio coding/decoding transformation coefficients and filtering coefficients cannot be freely adjusted by the user. As a consequence, even if the quality of the received audio on the receiving side is unsatisfactory, measures for improving the quality cannot be taken on the transmitting side.